1. Field of the Invention
The present invention relates to an improved vertically oriented vortex reactor system that includes an easily replaced wear plate at the entrance of the vortex reactor to control erosion of the reactor, and a recycle loop that leads into a supersonic jet of an ejector at an acute angle to return solids that minimizes the turbulence loses and maximizes the conservation of kinetic energy of the recycled stream, and removes tramp metals and other nonpyrolyzable debris from the recycle loop through a two 2-way or three-way valve system.
2. Description of the Prior Art
In general, in a vortex reactor system, dried feedstock is fed into a vortex pyrolysis reactor and the feed is ablatively pyrolyzed to maximize the yields of low molecular weight vapors. This is a carefully control led pyrolysis process to minimize thermal cracking of the vapors to light gases and minimize char formation.
The prior art vortex reactor uses a method of heat transfer involving the conduction of heat across a very thin film of pyrolysis oil, and the feed is entrained with carrier gases at very high velocities into the vortex reactor in a tangential direction. This causes the feed to be subjected to very high centrifugal forces, as the feed takes a helical path through the reactor. These centrifugal forces keep the feed particles on or bouncing very close to the externally heated vortex reactor wall, and as the feed slides on the inside surface of the reactor, the surface of the feed is rapidly heated and undergoes extremely rapid pyrolysis. When biomass is heated this rapidly, it undergoes chemical reactions which favor depolymerization or apparent melting, rather than the formation of char. If this melt is pushed aside or otherwise removed as it forms, the pryolsis front can be forced through the feed at rates that are far in excess of those that would be achieved by conventional heating techniques, to the point where the movement of the pyrolysis front could be as high as 3 cm/s.
The explanation for this rapid heat transfer is that it is by conduction across a very thin film of pyrolysis oil (estimated to be as thin as 30 micrometers). Since the wood depolymerizes very rapidly above 450.degree. C., ablative pyrolysis occurs quite rapidly at reactor wall temperatures above this temperature, i.e., at 625.degree. C. In the vortex reactor, it appears that the feed particles slide on a film of lubricating pyrolysis oil on the wall of the reactor. The thickness of the pyrolysis oil film is reduced with an increase in the pressure applied to the particle, which increases the conductive heat transfer across the film and the rate of pyrolysis of the particle. In the vortex reactor, the pressure applied to the particle is created by centrifugal forces pushing the particle onto the wall.
Since the centrifugal forces are proportional to the particle velocity squared, it is very important to have very high entering velocities for the feed particles. However, with high particle velocities, the residence time of the particle in the vortex reactor is very short, and this necessitates recycling of the partially pyrolyzed particles. This is readily done with a tangential exit at the end of the vortex reactor where a supersonic ejector is used to provide the suction to drive the recycle loop and to accelerate the particles to high velocities (subsonic).
In the prior art process; a small amount of char is formed in the vortex reactor. During recycle of the solids in the vortex reactor the char is attrited to a fine powder, which could be used as fuel in the pyrolysis furnace along with the waste gases. The pyrolysis vapors, carrier gas, and finely attrited char leave through an axial exit of the vortex reactor. The fine char is removed from the pyrolysis gases in a hot cyclone separator. The walls of the vortex reactor are heated to 625.degree. C., which results in a temperature of about 500.degree. C. in the exiting process stream.
A circulating fluidized bed reactor comprising a separator including a vortex chamber adjacent the top of the reactor for separating solid material from gases is disclosed in U.S. Pat. No. 4,934,281; however, this patent is essentially two inertial separation devices in series, wherein the solids separation is affected in two concentric cyclonic devices, operating sequentially on a gas stream, and a recirculating fluidized bed supplies the stream of particle laden gases (flowing in a downward direction) to a horizontally oriented vortex tube for separation.
U.S. Pat. No. 4,055,486 discloses apparatus for handling solid fluidized particles in carrying out a pyrolysis process. This process, nevertheless, is a complex system of two cyclonic separators in series to recover solids from a flue gas stream, as part of a dual-fluidized-bed pyrolysis system.
Apparatus for removal of entrained oil from solid particles from a flash pyrolysis is disclosed in U.S. Pat. No. 4,116,825. In this patent, the hot particles are a mixture of low density char and high density sintered or fused ash particles.
A method and apparatus for removing coarse unentrained char particles from the second stage of a two-stage gasifier is disclosed in U.S. Pat. No. 3,945,809. In essence, this patent describes a dual-fluidized bed coal pyrolysis unit, in which oxygen is used to partially oxidize coal char for a heat source.
U.S. Pat. No. 4,664,139 is directed to a slide valve for use with hot, abrasive flows of solids, such as in a fluidized catalytic cracking unit. The valve is specifically designed to exercise variable control of the flow of solids by virtue of a variable orifice area, in which the orifice configuration is a tear-drop shaped hole in a sliding plug of the valve.
None of the foregoing prior art provides means for removing stopped tramp metal and other inert material that has travelled part of the way of the vortex reactor length, due to a combination of low entering velocity and high friction of the inert particles with the wall of the reactor. Moreover, once a first particle stops, it acts as a dam to stop additional particles, and this stoppage causes part of the inside surface of the reactor to be covered with the stopped particles, thereby interfering with the heat transfer to moving particles.
Further, the prior art systems for utilizing a vortex reactor to affect pyrolysis, particularly where, instead of clean biomass, the feeding materials are Refuse Derived Fuel (RDF), there is very rapid erosion rates just opposite the tangential entrance, where some of the particles enter on a short chord, and the erosion pattern is very localized.
Further still, the prior art provides no solutions against returned recycle solids and gases past the colder feeder adaptor, which results in the deposit of condensed pyrolysis oil which slowly forms char that breaks off in large pieces and clogs the feeder adaptor and/or the recycle loop.
Finally, the prior art apparatus for vortex reactor systems, depending upon the feedstock, introduces metal and/or abrasive materials with the feed into the vortex reactor, and these tramp metals do not pyrolyze and they are not easily attrited to fine powders and re-entrained with the gases leaving the axial outlet of the vortex reactor.